Supersonic Cooling with a Pulsed Inlet

ABSTRACT

A supersonic cooling system operates by pumping liquid without the need of a condenser. The compression system utilizes a compression wave in the generation of the cooling effect. An inlet of the system may be pulsed to reduce energy required of a pump. The evaporator of compression system operates in the critical flow regime where the pressure one or more evaporator tubes will remain almost constant and then ‘jump’ or ‘shock up’ to the ambient pressure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to cooling via a supersonicfluid flow cycle. More specifically, the present invention is related toa supersonic fluid flow cycle that utilizes a pulsed inlet.

2. Description of the Related Art

Vapor compression systems are used in many cooling applications such asair conditioning and industrial refrigeration. A vapor compressionsystem generally includes a compressor, a condenser, an expansiondevice, and an evaporator. In a prior art vapor compression system, agas in a saturated vapor state is compressed to raise the temperature ofthat gas, the gas then being in a superheated vapor state. Thecompressed gas is then run through a condenser and turned into a liquid,and heat is rejected from the system. The condensed and liquefied gas isthen taken through an expansion device, which drops the pressure and thecorresponding temperature. The resulting refrigerant is then boiled inan evaporator, with the refrigerant absorbing heat. The saturated vaporis then returned to the compressor.

FIG. 1 illustrates a vapor compression system 100 as might be found inthe prior art. In the prior art vapor compression system 100 of FIG. 1,compressor 110 compresses the gas to (approximately) 238 pounds persquare inch (PSI) and a temperature of 190° F. Condenser 120 thenliquefies the heated and compressed gas to (approximately) 220 PSI and117° F. The gas that was liquefied by the condenser 120 is then passedthrough the expansion valve 130 of FIG. 1. By passing the liquefied gasthrough expansion value 130, the pressure is dropped to (approximately)20 PSI.

A corresponding drop in temperature accompanies the drop in pressure,which is reflected as a temperature drop to (approximately) 34° F. inFIG. 1. The refrigerant that results from dropping the pressure andtemperature at the expansion value 130 is boiled at evaporator 140.Through boiling of the refrigerant by evaporator 140, a low temperaturevapor results. The vapor is illustrated in FIG. 1 as having atemperature of (approximately) 39° F. and a corresponding pressure of 20PSI.

The cycle carried out by the system 100 of FIG. 1 is an example of avapor compression cycle. Such a cycle generally results in a coefficientof performance (COP) between 2.4 and 3.5. The COP, as illustrated inFIG. 1, is the evaporator cooling power or capacity divided bycompressor power. It should be noted that the temperature and PSIreferences that are shown in FIG. 1 are exemplary and are for thepurpose of illustration only.

FIG. 2 illustrates the performance that might be expected of a vaporcompression system similar to that illustrated in FIG. 1. The COPillustrated in FIG. 2 corresponds to a typical home or automotive vaporcompression system operating at an ambient temperature of(approximately) 90° F. The COP shown in FIG. 2 corresponds to a vaporcompression system utilizing a fixed orifice tube system.

A system like that illustrated in FIG. 1 and FIG. 2 typically operatesat an efficiency rate or COP that is far below that of system potential.To compress gas in a conventional vapor compression system like thatillustrated in FIG. 1 (system 100) typically takes 1.75-2.50 kilowattsfor every 5 kilowatts of cooling power. This exchange rate is less thanoptimal and directly correlates to the rise in pressure times thevolumetric flow rate. Degraded performance is similarly and ultimatelyrelated to performance (or lack thereof) by the compressor 110.

Haloalkane refrigerants such as tetrafluoroethane (CH₂FCF₃) are inertgases that are commonly used as refrigerants in refrigerators andautomobile air conditioners. Tetrafluoroethane has also been used tocool over-clocked computers. These gases are referred to as R-134 gases.The volume of an R-134 gas can be 600-1000 times greater than itscorresponding liquid form. This multiplier shows that the theoreticalefficiency of a system utilizing an R-134 gas is much higher than iscurrently being realized, and evidences the need for an improved coolingsystem that more fully recognizes system potential and overcomestechnical barriers related to compressor performance.

SUMMARY OF THE CLAIMED INVENTION

A first claimed embodiment of the present invention is a system thatincludes a fluid flow path with a high pressure region and a lowpressure region. The fluid flow path transports a working fluid at avelocity that is greater than or equal to the speed of sound in thefluid as the fluid travels from the high pressure region of the fluidflow path to the low pressure region of the fluid flow path. A pump isused to facilitate the flow of fluid in the fluid flow path. Installinga pulsing valve in the fluid flow path to create a pulsed inlet to thehigh pressure region and reduce the energy required to generate a givencooling capacity. An optional resonance chamber may be installed in linewith the pulsing valve to further reduce the demand on the pump of thesystem to assist in the formation of a compression wave.

A second claimed embodiment of the present invention is a method thatincludes pumping a working fluid through a fluid flow path. The fluidflow path includes a low pressure region in which the fluid flows at acritical flow rate. A pulsing valve may be installed downstream from thepump and upstream from the low pressure region of the fluid flow path toreduce the mass flow requirement of the system. An optional resonancechamber may be installed in line with the pulsing valve to assist in theformation of a compression wave to further reduce the demand on thepump.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a vapor compression cooling system asmay be found in the prior art.

FIG. 2 is a pressure—enthalpy graph for a vapor compression coolingsystem like that illustrated in FIG. 1.

FIG. 3 is a schematic diagram of an embodiment of a supersonic coolingsystem with a pulsed inlet.

FIG. 4 is a sectional view of an evaporator tube/nozzle.

FIG. 5 is a graphical representation of the effect of the pulsed inleton the mass flow rate of a cooling system.

FIG. 6 shows the inlet pressure as a function of time.

DETAILED DESCRIPTION

FIG. 3 illustrates an exemplary supersonic cooling system 300 inaccordance with an embodiment of the present invention. The supersoniccooling system 300 does not need to compress a gas as otherwise occursat compressor 110 in a prior art vapor compression system 100 like thatshown in FIG. 1. Supersonic cooling system 300 operates by pumpingliquid. Because supersonic cooling system 300 pumps liquid, thecompression system 300 does not require the use a condenser 120 as doesthe prior art compression system 100 of FIG. 1. Compression system 300instead utilizes a compression wave. The evaporator of compressionsystem 300 operates in the critical flow regime where the pressure in anevaporator tube will remain almost constant and then ‘jump’ or ‘shockup’ to the ambient pressure.

The supersonic cooling system 300 of FIG. 3 recognizes a improvedefficiencies in that the pump 310 of the system 300 does not, nor doesit need to, draw as much power as the compressor 110 in a prior artcompression system 100 like that shown in FIG. 1. A compression systemdesigned according to an embodiment of the presently disclosed inventionmay recognize exponentially improved pumping efficiencies. For example,where a prior art compression system 100 may require 1.75-2.5 kilowattsfor every 5 kilowatts of cooling power, a system 300 like thatillustrated in FIG. 3 may pump liquid from 14.7 to 120 PSI with a pump310 drawing power at approximately 500 W.

The power demands on the pump 310 may be further reduced by adding anaccumulator 320 to the fluid flow path. Still further efficiency gainsmay be realized by installing a pulsing valve 330 and a resonancechamber 340 in the fluid flow path. As a result of these improvements inefficiency, system 300 may utilize many working fluids, including butnot limited to water.

The cycle of the supersonic cooling system 300 of FIG. 3 may begin withthe pump 310 pumping the working fluid into the accumulator 320. Theflow out of the accumulator 320 may be controlled by a pulsing valve330. An exemplary pulsed mass flow is illustrated in FIG. 5. Anexemplary pressure profile resulting from a pulsed flow is illustratedin FIG. 6.

The pulsing valve 330 opens and closes the fluid flow path from theaccumulator 320 and operates at a frequency that may be determined bythe characteristics of a given installation of the supersonic coolingcycle 300. The pulsing valve 330 may operate at a frequency of fromapproximately 10 Hz to approximately 100 Hz. It will be recognized bythose skilled in the art that many types of fluid control valves may beutilized as the pulsing valve 330. The pulsing valve 330 may have asolenoid or other control mechanism that opens and closes the pulsingvalve 330 at the desired frequency.

The utilization of the pulsing valve 330 establishes pressure waves inthe working fluid in the cooling system 300. The pulsing valve 330 mayreduce the mass flow rate in the system 300 by approximately 50%, andmay allow the system 300 to operate at a reduced pressure relative tosystems not utilizing a pulsing valve, thereby reducing the demands onthe pump 310.

Operation of the pump 310 establishes circulation of the working fluidin the fluid flow path of system 300. Pump 310 may raise the pressure ofthe working fluid being used by system 300 from, for example, 20 PSI to100 PSI or more, to establish a high pressure region of the system 300.The temperature of the working fluid may, at this inlet section of thesystem 300, be approximately 95° F.

To further reduce the energy required to operate the pump 310 togenerate a given cooling capacity, a resonance chamber 340 may beinstalled in line with the pulsing valve 330. The resonance chamber 340assists in the formation of a compression wave in the system 300. Theresonance chamber 340 may be situated between the pulsing valve 330 anda manifold 350 that feeds the evaporator 360. The manifold 350 maysupply one or more evaporator tubes or nozzles 400 (see FIG. 4) in theevaporator 360.

As the working fluid is introduced to the evaporator 360, the evaporator360 induces a pressure drop e.g., to approximately 5.5 PSI, to establisha low pressure region and a concurrent phase change that result in alowered temperature. The evaporator 360 of system 300 operates in thecritical flow regime of the working fluid, thereby establishing acompression wave that assist in the acceleration of the working fluid.

The evaporator 360 may also induce cavitation in the working fluid aspart of the phase change. The cavitation also serves to reduce the speedof sound in the working fluid. Further explanation of the cavitationeffect is provided below in the description of the evaporator nozzle400.

As the working fluid is accelerated and undergoes a pressure drop andphase change, the working fluid further ‘boils off’ in evaporator 360,providing the cold sink desired in the system 300. In embodiments inwhich the working fluid is water, the water may be cooled to 35-45° F.,or approximately 37° F. The working fluid exits the evaporator 360 viaevaporator tube 360 where the fluid is ‘shocked up’ to approximately 20PSI.

To facilitate the dissipation of heat in the system 300, the evaporator360 may be thermally coupled with a heat exchanger 370. The heatexchanger 370 may be thermally coupled with a coolant fluid used in thesystem 300, the coolant fluid being circulated around or through an areaor an object to be cooled. The working fluid of the system 300 may be ata temperature of approximately 90-100° F. after the working fluid exitsevaporator 360 and returns to the inlet of pump 310.

FIG. 4 illustrates a structure that may be used in one or moreembodiments of the evaporator tube or nozzle 400. A main body 410 of theevaporator nozzle 400 of FIG. 4 includes an inlet portion 420, a throatportion 430, and an expansion portion 440.

The inlet portion 420 receives the working fluid from the inlet sectionof the cooling system 300. The working fluid is directed into the throatportion 430. The throat portion 430 provides a duct of substantiallyconstant profile (normally circular) through its length through whichthe working fluid is forced. The expansion portion 440 provides anexpanding tube-like member wherein the diameter of the fluid flow pathprogressively increases between the throat portion 430 and the outlet ofthe expansion portion 440. The actual profile of the expansion portion440 may depend upon the specific working fluid to be used in the system300.

In operation, when the working fluid enters the throat portion 430, theworking fluid is accelerated to high speed. The inlet pressure and thediameter of the throat orifice may be selected so that the speed of theworking fluid at the entry of the throat portion 430 is approximatelythe speed of sound (Mach 1).

As the working fluid travels through the nozzle 400, the acceleration ofthe working fluid causes a sudden drop in pressure which results incavitation that commences at the boundary between the exit of the inletportion 420 and the entry to the throat portion 430. Cavitation is alsotriggered along the wall of the throat portion 430. Cavitation resultsin bubbles of the working fluid in the vapor phase being present withinthe fluid in the liquid phase, thereby providing a multi-phase workingfluid. The creation of such vapor bubbles requires the input of energyfor the input of latent heat of vaporization and as a result thetemperature falls. At the same time, the reduction in pressure togetherwith the working fluid achieving a multi-phase state causes the localspeed of sound in the working fluid to be lowered, with the result thatthe working fluid exits the throat portion 430 at a supersonic speed of,for example, Mach 1.1 or higher. It is noted that the reduction in thelocalized speed of sound changes the character of the flow fromtraditional incompressible flow to a regime more in character with highspeed nozzle flow.

As the working fluid travels within the expansion portion 440, thepressure remains at a low level and the fluid expands. As a result ofthe expansion, the flow accelerates further, reaching a speed on theorder of for example approximately Mach 3.

As the fluid accelerates and pressure is reduced, the local staticpressure drops, so that more vapor is generated from the surroundingliquid working fluid. As the working fluid moves below the saturationline, the cold sink required for the cooling method is generated and theflow behaves as if it was in an over expanded jet. Once the workingfluid has picked up sufficient heat, and due to frictional losses, thefluid shocks back to a subsonic condition and returns to ambientconditions.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. The descriptions are not intended to limit the scope of theinvention to the particular forms set forth herein. Thus, the breadthand scope of a preferred embodiment should not be limited by any of theabove-described exemplary embodiments. It should be understood that theabove description is illustrative and not restrictive. To the contrary,the present descriptions are intended to cover such alternatives,modifications, and equivalents as may be included within the spirit andscope of the invention as defined by the appended claims and otherwiseappreciated by one of ordinary skill in the art. The scope of theinvention should, therefore, be determined not with reference to theabove description, but instead should be determined with reference tothe appended claims along with their full scope of equivalents.

1. A supersonic cooling system, comprising: a pump facilitating a flowof a fluid through a fluid flow path, the fluid flow path having a highpressure region and a low pressure region, the pump transporting thefluid at a velocity that is greater than or equal to the speed of soundin the fluid as the fluid travels from the high pressure region to thelow pressure region; and a pulsing valve creating a pulsed inlet to thehigh pressure region of the fluid flow path, thereby reducing the massflow rate of the fluid and corresponding energy required for a givencooling capacity.
 2. The supersonic cooling system of claim 1, furtherincluding a resonance chamber situated downstream of the pulsing valveto assist in the formation of a compression wave.
 3. The supersoniccooling system of claim 1, further comprising an evaporator at the lowpressure region of the fluid flow path, the evaporator facilitating aphase change of the fluid.
 4. The supersonic cooling system of claim 3,wherein the evaporator includes an evaporator tube that maintains aconstant pressure of the fluid.
 5. The supersonic cooling system ofclaim 3, wherein fluid flow in the evaporator is in a critical flowregime of the fluid.
 6. The supersonic cooling system of claim 3,wherein the evaporator facilitates a fluid shock up to an elevatedpressure as the fluid exits the evaporator.
 7. The supersonic coolingsystem of claim 6, wherein the evaporator facilitates the fluid shock upto the elevated pressure at substantially constant enthalpy.
 8. Thesupersonic cooling system of claim 1, wherein the fluid flow pathdecreases a pressure of the fluid at substantially constant enthalpy. 9.The supersonic cooling system of claim 1, wherein the fluid includeswater.
 10. The supersonic cooling system of claim 1, further comprisinga heat exchanger to transfer heat to the fluid.
 11. A supersonic coolingmethod, comprising: pumping a fluid through a fluid flow path with theaid of a pump, the fluid flow path including a low pressure regionwherein the fluid flows at a critical flow rate; and pulsing a fluidinput to the fluid flow path through a pulsing valve situated downstreamfrom the pump and upstream from the low pressure region of the fluidflow path to reduce the mass flow rate of the fluid and correspondingpower required for a given cooling capacity.
 12. The supersonic coolingmethod of claim 11, further comprising generating a compression wave,wherein generation of the compression wave includes the use of aresonance chamber situated downstream of the pulsing valve.
 13. Thesupersonic cooling method of claim 11, further comprising generating aphase change in the fluid, wherein generating the phase change includesthe use of an evaporator that operates in the low pressure region of thefluid flow path.
 14. The supersonic cooling method of claim 13, whereinthe phase change occurs at least in part due to fluid flow within theevaporator being in a critical flow regime of the fluid.
 15. Thesupersonic cooling method of claim 13, wherein the fluid shocks up to anelevated pressure as the fluid exits the evaporator.
 16. The supersoniccooling method of claim 15, wherein the fluid shocks up to the elevatedpressure at substantially constant enthalpy.
 17. The supersonic coolingmethod of claim 11, further comprising transferring heat to the fluid,the transfer of heat accompanying a phase change of the fluid.
 18. Thesupersonic cooling method of claim 11, further comprising transferringheat to the fluid via a heat exchanger.
 19. The supersonic coolingmethod of claim 11, wherein the fluid flows from a high pressure regionto the low pressure region of the fluid flow path at substantiallyconstant enthalpy.
 20. The supersonic cooling method of claim 11,wherein the fluid flows at a velocity greater than or equal to the speedof sound in at least a portion of the fluid flow path between a highpressure region and the low pressure region.